Extreme Population I objects are found in spiral arms and consist of young objects, such as T Tauri stars, O stars, B stars, and stars newly arrived on the zero-age main sequence. It is the brilliant light – in particular, the intense ultraviolet radiation – from extreme Pop I stars that causes the spiral arms to glow to brightly. Older Population I objects include stars like the Sun.
All Population I stars are relatively rich in elements heavier than hydrogen and helium since they formed from clouds of gas and dust which contained the products of nucleosynthesis from previous generations of stars. The presence of heavy elements in protoplanetary disks is believed to be a key factor in the formation of planets, so that only Population I objects are expected to harbor planetary systems, and possibly life, similar to our own. See also population.
Related categories• TYPES OF STARS
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